Tooth x-rays provide new insights into bird origins

A team of researchers at École normale supérieure (ENS) de Lyon, France, and colleagues, has gained new insights into the evolution of birds by studying in detail the teeth of their closest prehistoric relatives. In a study published in the open access journal BMC Evolutionary Biology, the researchers describe how they used synchrotron, x-ray and other non-invasive technologies to look at fossilized teeth in unprecedented detail.

Antoine Louchart, the corresponding author at ENS de Lyon, said: “Using synchrotron technology we were able to make visible the internal structure of jaws and teeth at very high resolution, which allowed us to re-evaluate earlier statements based on macroscopic findings that bird teeth differed widely from typical theropod dinosaur teeth.”

Because some of the tissues that comprise teeth and jaws, such as enamel or bone, are well-preserved, this makes it easy to compare these fossils with the teeth of other extinct or living vertebrates, in this case non-avian archosaurs – which include dinosaurs, crocodiles, and birds – and mammals.

Antoine Louchart said: “Our research sheds light on the evolution of teeth and eventual tooth loss in birds by revealing for the first time many of the characteristics of the teeth of the ‘last’ toothed birds. Knowing these characteristics allows us to understand the course of their evolution across dinosaurs, and more widely across amniotes and tetrapods.”

The study is the first to examine in detail the dentitions of the so called ‘last’ toothed birds Ichthyornithiformes and Hesperornithiformes, the closest prehistoric relatives to modern birds. The dentitions – that is the arrangement, type, and number of the teeth – of extinct organisms can provide information about their diet, development and growth, as well as their position in the phylogenetic tree, which shows the proposed evolutionary relationships among various species that are believed to share a common ancestor.

The researchers focused on the two best documented species in the two genera, Ichthyornis dispar –marine birds – and Hesperornis regalis – flightless, foot-propelled divers. They showed that the teeth of Ichthyornis and Hesperornis were very differently shaped. For example, while both species had hooked teeth, which suggests that they may have adapted to hold fish and other slippery prey, Ichthyornis teeth also had sharp cutting edges that were far less developed in Hesperornis teeth.

This may suggest that Ichthyornis cut its prey to pieces before swallowing it while Hesperornis swallowed it whole. Both Ichthyornis and Hesperornis teeth had very thin and simple enamel, which may indicate a loss of enamel on the way to tooth loss in modern birds. However, the researchers caution that this hypothesis will need to be tested by further analysis of avian teeth.

By revealing and comparing details of tooth shape, growth, attachment to the jaw and replacement in Ichthyornis, Hesperornis and other avian and non-avian organisms, the researchers show that many dental characteristics do not – as previously believed – differ radically between dinosaurs, birds and crocodilians. This suggests that characteristics previously only observed in birds were actually more widespread.

According to the authors, this may refute a previous argument in the debate on bird origins that the dental characteristics of Ichthyornis and Hesperornis provided evidence that birds may be non-dinosaurian in origin.

Please name the journal in any story you write. If you are writing for the web, please link to the article. All articles are available free of charge, according to BioMed Central's open access policy.

2. BMC Evolutionary Biology is an open access, peer-reviewed journal that considers articles on all aspects of molecular and non-molecular evolution of all organisms, as well as phylogenetics and palaeontology.

3. BioMed Central is an STM (Science, Technology and Medicine) publisher which has pioneered the open access publishing model. All peer-reviewed research articles published by BioMed Central are made immediately and freely accessible online, and are licensed to allow redistribution and reuse. BioMed Central is part of Springer Nature, a major new force in scientific, scholarly, professional and educational publishing, created in May 2015 through the combination of Nature Publishing Group, Palgrave Macmillan, Macmillan Education and Springer Science+Business Media.